/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.editor;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.util.SimplifiedVisitor;

import java.util.Arrays;

/**
 * This AttributeVisitor accumulates specified changes to local variables, and then applies these accumulated changes to
 * the code attributes that it visits.
 *
 * @author Eric Lafortune
 */
public class VariableEditor extends SimplifiedVisitor implements AttributeVisitor {
    private boolean modified;

    private boolean[] deleted = new boolean[ClassConstants.TYPICAL_VARIABLES_SIZE];
    private int[] variableMap = new int[ClassConstants.TYPICAL_VARIABLES_SIZE];

    private final VariableRemapper variableRemapper = new VariableRemapper();

    /**
     * Resets the accumulated code changes.
     * 
     * @param maxLocals the length of the local variable frame that will be edited next.
     */
    public void reset(int maxLocals) {
        // Try to reuse the previous array.
        if (deleted.length < maxLocals) {
            // Create a new array.
            deleted = new boolean[maxLocals];
        } else {
            // Reset the array.
            Arrays.fill(deleted, 0, maxLocals, false);
        }

        modified = false;
    }

    /**
     * Remembers to delete the given variable.
     * 
     * @param variableIndex the index of the variable to be deleted.
     */
    public void deleteVariable(int variableIndex) {
        deleted[variableIndex] = true;

        modified = true;
    }

    /**
     * Returns whether the given variable at the given offset will be deleted.
     */
    public boolean isDeleted(int instructionOffset) {
        return deleted[instructionOffset];
    }

    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
        // Avoid doing any work if nothing is changing anyway.
        if (!modified) {
            return;
        }

        int oldMaxLocals = codeAttribute.u2maxLocals;

        // Make sure there is a sufficiently large variable map.
        if (variableMap.length < oldMaxLocals) {
            variableMap = new int[oldMaxLocals];
        }

        // Fill out the variable map.
        int newVariableIndex = 0;
        for (int oldVariableIndex = 0; oldVariableIndex < oldMaxLocals; oldVariableIndex++) {
            variableMap[oldVariableIndex] = deleted[oldVariableIndex] ? -1 : newVariableIndex++;
        }

        // Set the map.
        variableRemapper.setVariableMap(variableMap);

        // Remap the variables.
        variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);

        // Update the length of local variable frame.
        codeAttribute.u2maxLocals = newVariableIndex;
    }
}
